arch/x86/kernel/realmode.c

#include <linux/io.h>
#include <linux/memblock.h>

#include <asm/cacheflush.h>
#include <asm/pgtable.h>
#include <asm/realmode.h>

unsigned char *real_mode_base;
struct real_mode_header real_mode_header;

void __init setup_real_mode(void)
{
	phys_addr_t mem;
	u16 real_mode_seg;
	u32 *rel;
	u32 count;
	u32 *ptr;
	u16 *seg;
	int i;

	struct real_mode_header *header =
		(struct real_mode_header *) real_mode_blob;

	size_t size = PAGE_ALIGN(header->end);

	/* Has to be in very low memory so we can execute real-mode AP code. */
	mem = memblock_find_in_range(0, 1<<20, size, PAGE_SIZE);
	if (!mem)
		panic("Cannot allocate trampoline\n");

	real_mode_base = __va(mem);
	memblock_reserve(mem, size);

	printk(KERN_DEBUG "Base memory trampoline at [%p] %llx size %zu\n",
	       real_mode_base, (unsigned long long)mem, size);

	memcpy(real_mode_base, real_mode_blob, size);

	real_mode_seg = __pa(real_mode_base) >> 4;
	rel = (u32 *) real_mode_relocs;

	/* 16-bit segment relocations. */
	count = rel[0];
	rel = &rel[1];
	for (i = 0; i < count; i++) {
		seg = (u16 *) (real_mode_base + rel[i]);
		*seg = real_mode_seg;
	}

	/* 32-bit linear relocations. */
	count = rel[i];
	rel =  &rel[i + 1];
	for (i = 0; i < count; i++) {
		ptr = (u32 *) (real_mode_base + rel[i]);
		*ptr += __pa(real_mode_base);
	}

	/* Copied header will contain relocated physical addresses. */
	memcpy(&real_mode_header, real_mode_base,
	       sizeof(struct real_mode_header));
}

/*
 * set_real_mode_permissions() gets called very early, to guarantee the
 * availability of low memory.  This is before the proper kernel page
 * tables are set up, so we cannot set page permissions in that
 * function.  Thus, we use an arch_initcall instead.
 */
static int __init set_real_mode_permissions(void)
{
	size_t all_size =
		PAGE_ALIGN(real_mode_header.end) -
		__pa(real_mode_base);

	set_memory_x((unsigned long) real_mode_base, all_size >> PAGE_SHIFT);
	return 0;
}

arch_initcall(set_real_mode_permissions);